Non-invasive imaging of the vascular system with the aid of computed tomography (CT) and magnetic resonance imaging (MRI) has become a well-established alternative to invasive intra-arterial angiography. Both CT and MRI provide high-resolution volumetric data sets that can be used for visualizing anatomical objects (internal organs, bones and joints, blood vessels, etc.) and pathological structures in the interior of a patient's body to be examined. These data, however, may contain many objects of less or even no diagnostic interest. This makes clinically relevant volume rendering—i.e., Maximum Intensity Projection (MIP), ray casting, Shaded Surface Display (SSD)—without preprocessing often difficult or even impossible.
Visualization of 3D tubular structures, such as e.g. blood vessels, is an important topic in CT- and MRI-based medical imaging. One way to display such 3D tubular structures for diagnostic purposes is to generate longitudinal cross-sections so as to show their lumen, wall, and surrounding tissue in a curved visualization plane. This process is called Curved Planar Reformation (CPR). A curved planar reformat—also known as a “curved planar reconstruction”—is a graphical visualization of a 3D tubular structure's longitudinal cross-section on such a curved visualization plane. The goal of curved reformatting is to make the tubular structure to be graphically displayed and examined visible in its entire length within a single image and without spatial foreshortening. To accomplish this requirement, a-priori information about the tubular structure, notably the 3D object's centerline, is required.
In particular, Curved Planar Reformation (CPR) is a way to visualize vascular structures with small diameter. Thereby, high-level information, such as e.g. a blood vessel's centerline (in the following also referred to as “central axis”), is used to resample and visualize image data which have previously been acquired by CT or MR angiography. Without loss of generality, the vessel's centerline is assumed to be a sequence of points at sub-voxel resolution. In general, the spatial position and shape of the centerline determines which parts of the 3D space are visualized. Using this technique, the whole length of the blood vessel is displayed within a single image. Vascular abnormalities (i.e., ulcerated stenoses, occlusions, aneurysms and vessel wall calcifications) can then be investigated by a physician. Current CPR techniques allow an investigation of a vessel lumen in a longitudinal section through the central axis of the vessel. In case vascular abnormalities are not touched by this plane and therefore do not appear in the generated image, the resampled plane is rotated around the central axis. This results in a set of images to be interpreted by the radiologist. Alternatively, a thick curved multiplanar reformat (CMPR) can be used.
Another aspect in today's computed tomography angiography is efficient visualization of treelike vascular structures using CPR display techniques. Multipath CPR techniques based on a projective combination of vessel segments provide a spatially coherent display of a patient's vascular anatomy. Thereby, however, parts of the arteries might be superimposed by other arteries depending on the respectively selected intersecting plane. For a detailed inspection of the entire vascular tree, different sections through the vessel's central axis have to be resampled.